Encapsulation methods for interferometric modulator and MEMS devices

ABSTRACT

Methods and devices used for the encapsulation of MEMS devices, such as an interferometric modulator, are disclosed. Encapsulation is provided to MEMS devices to protect the devices from such environmental hazards as moisture and mechanical shock. In addition to the encapsulation layer providing protection from environmental hazards, the encapsulation layer is additionally planarized so as to function as a substrate for additional circuit elements formed above the encapsulation layer.

BACKGROUND

1. Field of the Invention

The field relates to microelectromechanical systems (MEMS), and moreparticularly to methods of encapsulation of MEMS devices.

2. Description of the Related Technology

Microelectromechanical systems (MEMS) include micro mechanical elements,actuators, and electronics. Micromechanical elements may be createdusing deposition, etching, and or other micromachining processes thatetch away parts of substrates and/or deposited material layers or thatadd layers to form electrical and electromechanical devices. One type ofMEMS device is called an interferometric modulator. As used herein, theterm interferometric modulator or interferometric light modulator refersto a device that selectively absorbs and/or reflects light using theprinciples of optical interference. In certain embodiments, aninterferometric modulator may comprise a pair of conductive plates, oneor both of which may be transparent and/or reflective in whole or partand capable of relative motion upon application of an appropriateelectrical signal. In a particular embodiment, one plate may comprise astationary layer deposited on a substrate and the other plate maycomprise a metallic membrane separated from the stationary layer by anair gap. As described herein in more detail, the position of one platein relation to another can change the optical interference of lightincident on the interferometric modulator. Such devices have a widerange of applications, and it would be beneficial in the art to utilizeand/or modify the characteristics of these types of devices so thattheir features can be exploited in improving existing products andcreating new products that have not yet been developed.

SUMMARY OF CERTAIN EMBODIMENTS

The system, method, and devices of the invention each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this invention, its moreprominent features will now be discussed briefly. After considering thisdiscussion, and particularly after reading the section entitled“Detailed Description of Certain Embodiments” one will understand howthe features of this invention provide advantages over other displaydevices.

One aspect is a microelectromechanical system (MEMS) device, including asubstrate, a MEMS element on the substrate, the MEMS element including amovable component, an encapsulation layer encapsulating the MEMSelement, where the encapsulation layer is planarized, and an electronicelement on or over the encapsulation layer.

Another aspect is a method of manufacturing a microelectromechanicalsystem (MEMS) device, the method including forming a MEMS element on asubstrate, the MEMS element including a gap, forming an encapsulationlayer encapsulating the MEMS element, planarizing the encapsulationlayer, and forming an electronic element on the encapsulation layer.

Another aspect is a microelectromechanical system (MEMS) device,including means for supporting a MEMS element, the MEMS elementincluding a movable component, means for encapsulating the MEMS element,where the encapsulating means is planarized, and means for processingelectronic signals on or over the encapsulating means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view depicting a portion of one embodiment of aninterferometric modulator display in which a movable reflective layer ofa first interferometric modulator is in a relaxed position and a movablereflective layer of a second interferometric modulator is in an actuatedposition.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device incorporating a 3×3 interferometric modulator display.

FIGS. 3A and 3B are system block diagrams illustrating an embodiment ofa visual display device comprising a plurality of interferometricmodulators.

FIG. 4A is a cross section of the device of FIG. 1.

FIG. 4B is a cross section of an alternative embodiment of aninterferometric modulator.

FIG. 4C is a cross section of another alternative embodiment of aninterferometric modulator.

FIG. 4D is a cross section of yet another alternative embodiment of aninterferometric modulator.

FIG. 4E is a cross section of an additional alternative embodiment of aninterferometric modulator.

FIG. 5 is a cross section of a MEMS device comprising a encapsulationlayer, which is planarized.

FIGS. 6A-6H are cross sections of a MEMS device showing processing stepsused to manufacture the MEMS device of FIG. 5.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

The following detailed description is directed to certain specificembodiments of the invention. However, the invention can be embodied ina multitude of different ways. In this description, reference is made tothe drawings wherein like parts are designated with like numeralsthroughout. As will be apparent from the following description, theembodiments may be implemented in any device that is configured todisplay an image, whether in motion (e.g., video) or stationary (e.g.,still image), and whether textual or pictorial. More particularly, it iscontemplated that the embodiments may be implemented in or associatedwith a variety of electronic devices such as, but not limited to, mobiletelephones, wireless devices, personal data assistants (PDAs), hand-heldor portable computers, GPS receivers/navigators, cameras, MP3 players,camcorders, game consoles, wrist watches, clocks, calculators,television monitors, flat panel displays, computer monitors, autodisplays (e.g., odometer display, etc.), cockpit controls and/ordisplays, display of camera views (e.g., display of a rear view camerain a vehicle), electronic photographs, electronic billboards or signs,projectors, architectural structures, packaging, and aestheticstructures (e.g., display of images on a piece of jewelry). MEMS devicesof similar structure to those described herein can also be used innon-display applications such as in electronic switching devices.

Embodiments provide methods and devices which provide encapsulation toMEMS devices to protect the devices from such environmental hazards asmoisture and mechanical shock. In addition to the encapsulation layerproviding protection from environmental hazards, the encapsulation layeris additionally planarized so as to function as a substrate foradditional circuit elements formed above the encapsulation layer.

One interferometric modulator display embodiment comprising aninterferometric MEMS display element is illustrated in FIG. 1. In thesedevices, the pixels are in either a bright or dark state. In the bright(“on” or “open”) state, the display element reflects a large portion ofincident visible light to a user. When in the dark (“off” or “closed”)state, the display element reflects little incident visible light to theuser. Depending on the embodiment, the light reflectance properties ofthe “on” and “off” states may be reversed. MEMS pixels can be configuredto reflect predominantly at selected colors, allowing for a colordisplay in addition to black and white.

FIG. 1 is an isometric view depicting two adjacent pixels in a series ofpixels of a visual display, wherein each pixel comprises a MEMSinterferometric modulator. In some embodiments, an interferometricmodulator display comprises a row/column array of these interferometricmodulators. Each interferometric modulator includes a pair of reflectivelayers positioned at a variable and controllable distance from eachother to form a resonant optical gap with at least one variabledimension. In one embodiment, one of the reflective layers may be movedbetween two positions. In the first position, referred to herein as therelaxed position, the movable reflective layer is positioned at arelatively large distance from a fixed partially reflective layer. Inthe second position, referred to herein as the actuated position, themovable reflective layer is positioned more closely adjacent to thepartially reflective layer. Incident light that reflects from the twolayers interferes constructively or destructively depending on theposition of the movable reflective layer, producing either an overallreflective or non-reflective state for each pixel.

The depicted portion of the pixel array in FIG. 1 includes two adjacentinterferometric modulators 12 a and 12 b. In the interferometricmodulator 12 a on the left, a movable reflective layer 14 a isillustrated in a relaxed position at a predetermined distance from anoptical stack 16 a, which includes a partially reflective layer. In theinterferometric modulator 12 b on the right, the movable reflectivelayer 14 b is illustrated in an actuated position adjacent to theoptical stack 16 b.

The optical stacks 16 a and 16 b (collectively referred to as opticalstack 16), as referenced herein, typically comprise several fusedlayers, which can include an electrode layer, such as indium tin oxide(ITO), a partially reflective layer, such as chromium, and a transparentdielectric. The optical stack 16 is thus electrically conductive,partially transparent, and partially reflective, and may be fabricated,for example, by depositing one or more of the above layers onto atransparent substrate 20. The partially reflective layer can be formedfrom a variety of materials that are partially reflective such asvarious metals, semiconductors, and dielectrics. The partiallyreflective layer can be formed of one or more layers of materials, andeach of the layers can be formed of a single material or a combinationof materials.

In some embodiments, the layers of the optical stack 16 are patternedinto parallel strips, and may form row electrodes in a display device asdescribed further below. The movable reflective layers 14 a, 14 b may beformed as a series of parallel strips of a deposited metal layer orlayers (orthogonal to the row electrodes of 16 a, 16 b) deposited on topof posts 18 and an intervening sacrificial material deposited betweenthe posts 18. When the sacrificial material is etched away, the movablereflective layers 14 a, 14 b are separated from the optical stacks 16 a,16 b by a defined gap 19. A highly conductive and reflective materialsuch as aluminum may be used for the reflective layers 14, and thesestrips may form column electrodes in a display device.

With no applied voltage, the gap 19 remains between the movablereflective layer 14 a and optical stack 16 a, with the movablereflective layer 14 a in a mechanically relaxed state, as illustrated bythe pixel 12 a in FIG. 1. However, when a potential difference isapplied to a selected row and column, the capacitor formed at theintersection of the row and column electrodes at the corresponding pixelbecomes charged, and electrostatic forces pull the electrodes together.If the voltage is high enough, the movable reflective layer 14 isdeformed and is forced against the optical stack 16. A dielectric layer(not illustrated in this Figure) within the optical stack 16 may preventshorting and control the separation distance between layers 14 and 16,as illustrated by pixel 12 b on the right in FIG. 1. The behavior is thesame regardless of the polarity of the applied potential difference. Inthis way, row/column actuation that can control the reflective vs.non-reflective pixel states is analogous in many ways to that used inconventional LCD and other display technologies.

FIGS. 2 through 5B illustrate one exemplary process and system for usingan array of interferometric modulators in a display application.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device that may incorporate aspects of the invention. In theexemplary embodiment, the electronic device includes a processor 21which may be any general purpose single- or multi-chip microprocessorsuch as an ARM, Pentium®, Pentium II®, Pentium III®, Pentium IV®,Pentium® Pro, an 8051, a MIPS®, a Power PC®, an ALPHA®, or any specialpurpose microprocessor such as a digital signal processor,microcontroller, or a programmable gate array. As is conventional in theart, the processor 21 may be configured to execute one or more softwaremodules. In addition to executing an operating system, the processor maybe configured to execute one or more software applications, including aweb browser, a telephone application, an email program, or any othersoftware application.

In one embodiment, the processor 21 is also configured to communicatewith an array driver 22. In one embodiment, the array driver 22 includesa row driver circuit 24 and a column driver circuit 26 that providesignals to a display array or panel 30. The cross section of the arrayillustrated in FIG. 1 is shown by the lines 1-1 in FIG. 2.

FIGS. 3A and 3B are system block diagrams illustrating an embodiment ofa display device 40. The display device 40 can be, for example, acellular or mobile telephone. However, the same components of displaydevice 40 or slight variations thereof are also illustrative of varioustypes of display devices such as televisions and portable media players.

The display device 40 includes a housing 41, a display 30, an antenna43, a speaker 45, an input device 48, and a microphone 46. The housing41 is generally formed from any of a variety of manufacturing processesas are well known to those of skill in the art, including injectionmolding and vacuum forming. In addition, the housing 41 may be made fromany of a variety of materials, including, but not limited to, plastic,metal, glass, rubber, and ceramic, or a combination thereof In oneembodiment, the housing 41 includes removable portions (not shown) thatmay be interchanged with other removable portions of different color, orcontaining different logos, pictures, or symbols.

The display 30 of exemplary display device 40 may be any of a variety ofdisplays, including a bi-stable display, as described herein. In otherembodiments, the display 30 includes a flat-panel display, such asplasma, EL, OLED, STN LCD, or TFT LCD as described above, or anon-flat-panel display, such as a CRT or other tube device, as is wellknown to those of skill in the art. However, for purposes of describingthe present embodiment, the display 30 includes an interferometricmodulator display, as described herein.

The components of one embodiment of exemplary display device 40 areschematically illustrated in FIG. 3B. The illustrated exemplary displaydevice 40 includes a housing 41 and can include additional components atleast partially enclosed therein. For example, in one embodiment, theexemplary display device 40 includes a network interface 27 thatincludes an antenna 43, which is coupled to a transceiver 47. Thetransceiver 47 is connected to a processor 21, which is connected toconditioning hardware 52. The conditioning hardware 52 may be configuredto condition a signal (e.g., filter a signal). The conditioning hardware52 is connected to a speaker 45 and a microphone 46. The processor 21 isalso connected to an input device 48 and a driver controller 29. Thedriver controller 29 is coupled to a frame buffer 28 and to an arraydriver 22, which in turn is coupled to a display array 30. A powersupply 50 provides power to all components as required by the particularexemplary display device 40 design.

The network interface 27 includes the antenna 43 and the transceiver 47so that the exemplary display device 40 can communicate with one or moredevices over a network. In one embodiment, the network interface 27 mayalso have some processing capabilities to relieve requirements of theprocessor 21. The antenna 43 is any antenna known to those of skill inthe art for transmitting and receiving signals. In one embodiment, theantenna transmits and receives RF signals according to the IEEE 802.11standard, including IEEE 802.11(a), (b), or (g). In another embodiment,the antenna transmits and receives RF signals according to the BLUETOOTHstandard. In the case of a cellular telephone, the antenna is designedto receive CDMA, GSM, AMPS, or other known signals that are used tocommunicate within a wireless cell phone network. The transceiver 47pre-processes the signals received from the antenna 43 so that they maybe received by and further manipulated by the processor 21. Thetransceiver 47 also processes signals received from the processor 21 sothat they may be transmitted from the exemplary display device 40 viathe antenna 43.

In an alternative embodiment, the transceiver 47 can be replaced by areceiver. In yet another alternative embodiment, network interface 27can be replaced by an image source, which can store or generate imagedata to be sent to the processor 21. For example, the image source canbe a digital video disc (DVD) or a hard-disc drive that contains imagedata, or a software module that generates image data.

Processor 21 generally controls the overall operation of the exemplarydisplay device 40. The processor 21 receives data, such as compressedimage data from the network interface 27 or an image source, andprocesses the data into raw image data or into a format that is readilyprocessed into raw image data. The processor 21 then sends the processeddata to the driver controller 29 or to frame buffer 28 for storage. Rawdata typically refers to the information that identifies the imagecharacteristics at each location within an image. For example, suchimage characteristics can include color, saturation, and gray-scalelevel.

In one embodiment, the processor 21 includes a microcontroller, CPU, orlogic unit to control operation of the exemplary display device 40.Conditioning hardware 52 generally includes amplifiers and filters fortransmitting signals to the speaker 45, and for receiving signals fromthe microphone 46. Conditioning hardware 52 may be discrete componentswithin the exemplary display device 40, or may be incorporated withinthe processor 21 or other components.

The driver controller 29 takes the raw image data generated by theprocessor 21 either directly from the processor 21 or from the framebuffer 28 and reformats the raw image data appropriately for high speedtransmission to the array driver 22. Specifically, the driver controller29 reformats the raw image data into a data flow having a raster-likeformat, such that it has a time order suitable for scanning across thedisplay array 30. Then the driver controller 29 sends the formattedinformation to the array driver 22. Although a driver controller 29,such as a LCD controller, is often associated with the system processor21 as a stand-alone Integrated Circuit (IC), such controllers may beimplemented in many ways. They may be embedded in the processor 21 ashardware, embedded in the processor 21 as software, or fully integratedin hardware with the array driver 22.

Typically, the array driver 22 receives the formatted information fromthe driver controller 29 and reformats the video data into a parallelset of waveforms that are applied many times per second to the hundredsand sometimes thousands of leads coming from the display's x-y matrix ofpixels.

In one embodiment, the driver controller 29, array driver 22, anddisplay array 30 are appropriate for any of the types of displaysdescribed herein. For example, in one embodiment, driver controller 29is a conventional display controller or a bi-stable display controller(e.g., an interferometric modulator controller). In another embodiment,array driver 22 is a conventional driver or a bi-stable display driver(e.g., an interferometric modulator display). In one embodiment, adriver controller 29 is integrated with the array driver 22. Such anembodiment is common in highly integrated systems such as cellularphones, watches, and other small area displays. In yet anotherembodiment, display array 30 is a typical display array or a bi-stabledisplay array (e.g., a display including an array of interferometricmodulators).

The input device 48 allows a user to control the operation of theexemplary display device 40. In one embodiment, input device 48 includesa keypad, such as a QWERTY keyboard or a telephone keypad, a button, aswitch, a touch-sensitive screen, or a pressure- or heat-sensitivemembrane. In one embodiment, the microphone 46 is an input device forthe exemplary display device 40. When the microphone 46 is used to inputdata to the device, voice commands may be provided by a user forcontrolling operations of the exemplary display device 40.

Power supply 50 can include a variety of energy storage devices as arewell known in the art. For example, in one embodiment, power supply 50is a rechargeable battery, such as a nickel-cadmium battery or a lithiumion battery. In another embodiment, power supply 50 is a renewableenergy source, a capacitor, or a solar cell including a plastic solarcell, and solar-cell paint. In another embodiment, power supply 50 isconfigured to receive power from a wall outlet.

In some embodiments, control programmability resides, as describedabove, in a driver controller which can be located in several places inthe electronic display system. In some embodiments, controlprogrammability resides in the array driver 22. Those of skill in theart will recognize that the above-described optimizations may beimplemented in any number of hardware and/or software components and invarious configurations.

The details of the structure of interferometric modulators that operatein accordance with the principles set forth above may vary widely. Forexample, FIGS. 4A-4E illustrate five different embodiments of themovable reflective layer 14 and its supporting structures. FIG. 4A is across section of the embodiment of FIG. 1, where a strip of metalmaterial 14 is deposited on orthogonally extending supports 18. In FIG.4B, the moveable reflective layer 14 is attached to supports at thecorners only, on tethers 32. In FIG. 4C, the moveable reflective layer14 is suspended from a deformable layer 34, which may comprise aflexible metal. The deformable layer 34 connects, directly orindirectly, to the substrate 20 around the perimeter of the deformablelayer 34. These connections are herein referred to as support posts. Theembodiment illustrated in FIG. 4D has support post plugs 42 upon whichthe deformable layer 34 rests. The movable reflective layer 14 remainssuspended over the gap, as in FIGS. 4A-4C, but the deformable layer 34does not form the support posts by filling holes between the deformablelayer 34 and the optical stack 16. Rather, the support posts are formedof a planarization material, which is used to form support post plugs42. The embodiment illustrated in FIG. 4E is based on the embodimentshown in FIG. 4D, but may also be adapted to work with any of theembodiments illustrated in FIGS. 4A-4C, as well as additionalembodiments not shown. In the embodiment shown in FIG. 4E, an extralayer of metal or other conductive material has been used to form a busstructure 44. This allows signal routing along the back of theinterferometric modulators, eliminating a number of electrodes that mayotherwise have had to be formed on the substrate 20.

In embodiments such as those shown in FIG. 4, the interferometricmodulators function as direct-view devices, in which images are viewedfrom the front side of the transparent substrate 20, the side oppositeto that upon which the modulator is arranged. In these embodiments, thereflective layer 14 optically shields the portions of theinterferometric modulator on the side of the reflective layer oppositethe substrate 20, including the deformable layer 34. This allows theshielded areas to be configured and operated upon without negativelyaffecting the image quality. Such shielding allows the bus structure 44in FIG. 4E, which provides the ability to separate the opticalproperties of the modulator from the electromechanical properties of themodulator, such as addressing and the movements that result from thataddressing. This separable modulator architecture allows the structuraldesign and materials used for the electromechanical aspects and theoptical aspects of the modulator to be selected and to functionindependently of each other. Moreover, the embodiments shown in FIGS.4C-4E have additional benefits deriving from the decoupling of theoptical properties of the reflective layer 14 from its mechanicalproperties, which are carried out by the deformable layer 34. Thisallows the structural design and materials used for the reflective layer14 to be optimized with respect to the optical properties, and thestructural design and materials used for the deformable layer 34 to beoptimized with respect to desired mechanical properties.

The following description is directed to methods and devices used forthe encapsulation of MEMS devices, such as the interferometricmodulators described above. The encapsulation layers described hereinare applied to interferometric modulators, however, in other embodimentsencapsulation layers can be applied to other MEMS devices.

FIG. 5 is an illustration of an exemplary embodiment of a MEMS device100 comprising substrate 110 with MEMS element 120 thereon. Over theMEMS element 120 is encapsulation layer 130 with an electronic element140 thereon.

Substrate 110 supports the other components, and may, in someembodiments, be transparent or partially transparent. The substrate maybe formed of, for example, glass, plastic, another material, or acombination thereof. The substrate provides a means for supporting MEMSelement 120.

MEMS element 120 may be any MEMS device. For example, the MEMS elementmay be an interferometric modulator, a switch, or another MEMS element,or combination thereof In some embodiments, the MEMS element comprises agap and/or a moveable component. In some embodiments, the MEMS elementmay be any of the interferometric modulators described above and shownin FIGS. 4A-4E.

The MEMS element 120 is encapsulated by encapsulation layer 130.Encapsulation layer 130 may provide a hermetic seal for theinterferometric modulator in order to protect it from environmentalagents such as moisture and oxygen. The seal also allows for pressurewithin the MEMS element to be maintained independent from externalpressure of the ambient environment. Thus, the MEMS element may befabricated to maintain an environment that differs from the ambientenvironment. For example, during manufacturing, the encapsulation layer130 can be manufactured with a via 150 that provides an electricalconnection from the electronic element 140 to the MEMS element 120. Insome embodiments the encapsulation layer seals all interferometricmodulators in an array from the ambient environment, while in otherembodiments only a portion of the interferometric modulators are sealedby the encapsulation layer. For example, an array may comprise someinterferometric modulators which do not move. Such interferometricmodulators may have a reflective layer manufactured at a known fixedposition, and may not need to have encapsulation layer.

The encapsulation layer 130 may be formed of BCB, acrylic, polyimide,silicon oxide, silicon nitride, AlOx, oxynitride, etc.

When the moveable components of the MEMS element 120 move betweenvarious states, optional orifices within the MEMS element 120 (not shownin the cross-section of FIG. 5) allow for gases to flow between aroundor through the MEMS element 120. The viscosity of the gases within thedevice may slow the movement. Sealing the interferometric modulatorarray at the time of manufacturing with the encapsulation layer 130allows for deliberate customization of the environment of the MEMSelement 120. Because of the permanent nature of the encapsulationprovided by encapsulation layer 130, the environment within each MEMSelement 120 can persist throughout the lifetime of the array. Forexample, inducing a vacuum before sealing will substantially remove thegases from the MEMS element 120, so that during use, the movement of themoveable components is not impeded by the cavity atmosphere. It shouldbe realized that interferometric modulator arrays are typically sealedfrom the ambient environment by sealing a backplate to protect the arrayfrom the outside environment. While this type of sealant may still beused, it may also be unnecessary because the encapsulation layer 130 canalso serve to protect the interior cavities from being affected by theambient environment. Similarly, embodiments of the invention may alsoinclude the use of a desiccant to reduce the moisture levels within theMEMS element 120. However, the use of such desiccant may be unnecessaryin view of the fact that the MEMS element 120 may be hermetically sealedby the encapsulation layer 130. The encapsulation layer 130 provides ameans for sealing the MEMS element 120. The encapsulation layer 130 alsoprovides a means for supporting the electronic element 140.

As shown in FIG. 5, in some embodiments, the encapsulation layer 130comprises a via 150 which makes an electrical connection between theMEMS element 120 and the electronic element 140. The electronic element140 may comprise passive and/or active elements, such as routing wires,resistors, capacitors, inductors, diodes, and transistors. Theseelements may also include variable elements, such as variable resistorsand variable capacitors. The type of electronic element is not limitedand other types of electronic elements may also be used. The electronicelement may comprise display driver circuitry for at least one of rows,columns, portions of rows and/or columns, and individual deformablelayers. The electronic element may additionally or alternativelycomprise sense circuitry, used to determine the state of individualdeformable layers or groups (such as rows or columns) of deformablelayers. ESD protection, EM shielding, and interconnect routing may alsobe included in the electronic element. In some embodiments theelectronic element may also comprise digital signal processing (DSP)functions such as data filtering and control information decoding. Insome embodiments, the electronic element may comprise RF functions suchas an antenna and a power amp, as well as data converters. The type andfunction of the electronic element is not limited and other types andfunctions may be implemented. In some embodiments, the electronicelement provides a means for electrically communicating with the MEMSelement.

In order to prepare the encapsulation layer 130 for the electronicelement 140, the upper surface of the encapsulation layer 130 may beplanarized. A planarization process may be performed to modify the uppersurface of the encapsulation layer 130 so that it is substantiallyplanar. Planarization allows the electronic element 140 to be formedwithout the effects of topological irregularities which would exist inthe encapsulation layer 130 without the planarization. For someelectronic elements, such as TFT's, topological irregularities cansignificantly affect performance parameters. Accordingly, when an arrayof electronic elements 140 is to be formed on an encapsulation layer 130above an array of MEMS elements 110, planarization of the encapsulationlayer 130 results in more consistent performance of the TFT's across thearray.

FIGS. 6A-6E are cross sections of a MEMS device showing processing stepsused to manufacture the MEMS device of FIG. 5. These figures showprocessing steps for the interferometric modulator shown in FIG. 4D. Theprocessing steps may be analogously applied to other interferometricmodulator embodiments, for example, any of the interferometricmodulators shown in FIGS. 4A-4C, and 4E. Other processing steps can beused in addition to or alternatively.

FIG. 6A is a cross section of MEMS device 250 at a particular point inthe manufacturing process. MEMS device 250 at the point show has a MEMSelement 200 built on substrate 210. MEMS element 200 includes moveablelayer 214 supported on posts 242 and spaced apart from optical stack 216by a gap. Moveable layer 214 may be similar to layer 14 described above,posts 242 may be similar to support post plugs 42 described above, andoptical stack 216 may be similar to optical stack 16 described above.Also shown in FIG. 6A is sacrificial layer 220. The sacrificial layer220 is used to form the MEMS element 200, and is removed later in themanufacturing process.

FIG. 6B is a cross section of MEMS device 250 at a second point in themanufacturing process. A second sacrificial layer 225 has been formed onthe MEMS element 200. In FIG. 6C the second sacrificial layer 225 hasbeen etched in preparation for forming an encapsulation layer.

FIG. 6D is a cross section of MEMS device 250 showing MEMS element 200covered by encapsulation layer 300. The encapsulation layer 300 can beformed of BCB, acrylic, polyimide, silicon oxide, silicon nitride, AlOx,oxynitride, etc. After formation the encapsulation layer 300 istypically non-planar, as indicated by irregular sections 305.

Because the encapsulation layer 300 forms a substrate for electronicelements placed thereon, the topological irregularities can affect theperformance of some electronic elements. It is advantageous to perform aplanarization process on the encapsulation layer 300 to substantiallyremove the topological irregularities. FIG. 6E shows the encapsulationlayer 300 after planarization. The planarization process may include amechanical polishing (MP) process, a chemical mechanical planarization(CMP) process, or a spin-coating process.

In these embodiments, the encapsulation layer 300 is spaced apart fromthe relaxed state position of the moveable layer 214 by the secondsacrificial layer 225. The introduction of such a sacrificial layer mayimprove reliability of the device. During operation, the moveable layer214 may forcefully move from an actuated position close to the opticalstack 216 to the relaxed position away from the optical stack 216.Maintaining a space above the moveable layer 214 allows for the moveablelayer 214 to “overshoot” the final relaxed state because of themechanical restorative force. Without sufficient space, the deformablelayer would collide with the encapsulating layer 300, potentiallydamaging the structure and shortening the life of the encapsulatinglayer 300 and/or the mechanical interferometric modulator structure.

FIG. 6F shows MEMS device 250 where the encapsulation layer 300 hasholes 310, and the sacrificial layers 220 and 225 have been removed. Insome embodiments, the sacrificial layers 200 and 225 are removed throughthe holes 310 in the encapsulation layer 300. In some embodiments, theholes are used to create a desired environment for the MEMS element 200.For example, as discussed above, a substantial vacuum, or low pressureenvironment can be established with the holes 310.

FIG. 6G shows MEMS device 250 where the holes 310 in the encapsulationlayer 300 have been plugged. In some embodiments, the plugs are formedof a dielectric material. In some embodiments, the plugs are conductive.In some embodiments, the encapsulation layer 300 with plugged holes 310forms a hermetic seal for the MEMS element 200.

FIG. 6H shows MEMS device 250 with electronic element 400 formed on theencapsulation layer 300, which has been planarized. In this embodiment,electronic element 400 is a thin film transistor (TFT) having gate 410,insulator layer 415, semiconductor layer 420, source/drain layer 425,drain electrode 430, and source electrode 435. In this embodiment sourceelectrode 435 is connected to moveable layer 214 through encapsulationlayer 300. The electronic element 400 may comprise an interconnect layerand may comprise a connector configured to connect the MEMS device toanother device. The electronic element 400 may comprise either or bothof an active element and a passive element.

In various embodiments of the manufacturing process, the steps describedabove happen in a different order. For example, the encapsulation layer300 may be planarized after the material of the sacrificial layer(s) isremoved. The holes 310 may be plugged before the encapsulation layer 300is planarized. The electronic element 400 may be formed after theencapsulation layer 300 is planarized, and before the material of thesacrificial layer(s) is removed. Accordingly, the atmosphere of the MEMSelement 200 may be modified and the holes 310 plugged after theformation of the electronic element 300. In some embodiments, the holesmay be plugged with conductive material which connects the electronicelement 400 with the MEMS element 200.

While the above detailed description has shown, described, and pointedout novel features as applied to various embodiments, it will beunderstood that various omissions, substitutions, and changes in theform and details of the device or process illustrated may be made bythose skilled in the art without departing from the spirit of theinvention. As will be recognized, the present invention may be embodiedwithin a form that does not provide all of the features and benefits setforth herein, as some features may be used or practiced separately fromothers.

1. A microelectromechanical system (MEMS) device, comprising: asubstrate; a MEMS element on the substrate, the MEMS element comprisinga movable component; an encapsulation layer encapsulating the MEMSelement, wherein the encapsulation layer is planarized; and anelectronic element on or over the encapsulation layer.
 2. The device ofclaim 1, wherein the encapsulation layer is planarized with a chemicalmechanical planarization method.
 3. The device of claim 1, wherein theencapsulation layer is planarized with a mechanical polishing method. 4.The device of claim 1, wherein the MEMS element comprises aninterferometric modulator.
 5. The device of claim 1, wherein the MEMSelement comprises a moveable component configured to move between firstand second positions, the first position being nearer the encapsulationlayer than the second position.
 6. The device of claim 1, wherein theencapsulation layer is spaced apart from the MEMS element.
 7. The deviceof claim 1, wherein the encapsulation layer comprises a hole.
 8. Thedevice of claim 7, wherein the hole is plugged.
 9. The device of claim7, wherein the hole is plugged with a dielectric material.
 10. Thedevice of claim 7, wherein the hole is plugged with a conductivematerial.
 11. The device of claim 10, wherein the conductive material iselectrically connected to the MEMS element.
 12. The device of claim 1,wherein the electronic element comprises an interconnect layer.
 13. Thedevice of claim 1, wherein the electronic element comprises a connector.14. The device of claim 1, wherein the electronic element comprises anactive device.
 15. The device of claim 1, wherein the electronic elementcomprises a passive device.
 16. The device of claim 1, wherein theelectronic element comprises a thin film transistor.
 17. A method ofmanufacturing a microelectromechanical system (MEMS) device, the methodcomprising: forming a MEMS element on a substrate, the MEMS elementcomprising a gap; forming an encapsulation layer encapsulating the MEMSelement; planarizing said encapsulation layer; and forming an electronicelement on the encapsulation layer.
 18. The method of claim 17, whereinforming the encapsulation layer comprises forming a hole.
 19. The methodof claim 18, wherein forming the MEMS element comprises depositing asacrificial layer, and the method further comprises removing thesacrificial layer through the hole.
 20. The method of claim 19, whereinthe electronic element is formed prior to removing the sacrificiallayer.
 21. The method of claim 19, further comprising: modifying theenvironment of the MEMS element; and plugging the hole.
 22. The methodof claim 18, further comprising plugging the hole.
 23. The method ofclaim 22, further comprising plugging the hole, wherein theencapsulation layer is planarized after the hole is plugged.
 24. Themethod of claim 17, further comprising electrically connecting the MEMSelement with the electronic element through the encapsulation layer. 25.A microelectromechanical system (MEMS) device, comprising: means forsupporting a MEMS element, the MEMS element comprising a movablecomponent; means for encapsulating the MEMS element, wherein theencapsulating means is planarized; and means for processing electronicsignals on or over the encapsulating means.
 26. The device of claim 25,wherein the supporting means comprises a substrate, the encapsulatingmeans comprises an encapsulation layer, and the processing meanscomprises an electronic element.
 27. The device of claim 1, wherein theencapsulating means is planarized with a chemical mechanicalplanarization method.
 28. The device of claim 25, wherein theencapsulating means is planarized with a mechanical polishing method.29. The device of claim 25, wherein the MEMS element comprises aninterferometric modulator.
 30. The device of claim 25, wherein theencapsulating means comprises a hole.
 31. The device of claim 30,wherein the hole is plugged.
 32. The device of claim 31, wherein theprocessing means is electrically connected to the MEMS element throughthe hole.
 33. The device of claim 25, wherein the electronic elementcomprises a connector.
 34. The device of claim 25, wherein theprocessing means comprises a thin film transistor.